Many real-time applications, such as Voice over IP (VoIP), demand underlying infrastructures to both be reliable and provide acceptable quality-of-service (QoS). Ideally, converged IP networks (which simultaneously carry voice and data traffic) will be made as reliable as their circuit-based voice counterparts, despite the inherent limitations of IP networks. To attain this goal, protection is needed against network (hardware and software) failures, as well as appropriate forms of “QoS protection” against the inevitable losses and delays that occur in IP networks. VoIP is particularly vulnerable to such adverse performance occurrences. For example, link and router failures may be followed by long periods of routing instability and packet loss, which can heavily compromise the quality of VoIP. Even on good paths, rare loss events can occasionally cause perceptible degradation of voice quality.
There have been recent attempts in the network communications art to improve the reliability (hardware and software), performance (delay, jitter, and packet loss), and QoS characteristics of IP service provider networks. Multi-protocol label switching (MPLS) is one technique that has been investigated. An example of this technique is described in a paper entitled “Multiprotocol Label Switching Architecture” by E. Rosen, A. Viswanathan, and R. Callon (IETF RFC 3031), which is hereby incorporated by reference. MPLS provides the ability to separate routing from forwarding and assign incoming packets a label at a label edge router (LER). Packets are then forwarded along a label switch path (LSP) where forwarding decisions are based solely on the contents of the label. This provides for, among other things, path protection mechanisms that provide fail-over and redundancy, and traffic engineering capabilities (e.g., appropriate paths through the network can be selected to achieve desired performance characteristics for various traffic classes).
While such prior art improvements show promise in improving the reliability and performance of service provider (SP) networks, it is unclear how soon the various proposed techniques will be widely available to individual enterprise customers—and at what prices. Further, an enterprise may not want to depend solely on the “guarantees” of a single SP (e.g., in its disaster recovery planning). In addition, it is likely that many enterprise customers will desire connections to multiple service providers. Such a multi-homed configuration helps an enterprise maintain high availability and retain some control over its own network's protection.
One variation of a multi-homed configuration is a dual-homed configuration wherein typically in the prior art, the second service provider is just used as a backup for the primary service provider. In the event of a failure, the enterprise edge router, for example, simply diverts its traffic to the backup (secondary) service provider network. Sometimes, the enterprise network may use a portion of its link to the secondary service provider to carry some traffic. Usually, service providers have a fixed charge for the link from the enterprise to the service provider.
Some recent improvements in the prior art utilize “smart routing” techniques in dual-homed architectures, an example of which technique is described in an article entitled “Users Find a Smarter Way to Route” by T. Greene, appearing in NetworkWorld ((www.nwfusion.com), 22 Jul. 2002, p. 7), and incorporated herein by reference. In such a technique, even when there aren't any failures, both service provider networks might be used to carry the enterprise's traffic: some flows are sent over the first SP and some flows are sent over the second SP. By way of example, a “smart” edge router might send test/probe packets across a set of possible routes and then use route-control software to select a particular “best” route (based on the measured performance of each SP). The selected SP (and route) can change after each probe/measurement of network conditions, and the selection can be based on a given cost function. This is in contrast with common prior art routing schemes that often pick routes just to minimize the number of hops—not necessarily considering the best performance or the minimum cost.
With smart routing technology though, there are several issues to consider in its implementation. First, there is the challenge and complexity of determining the best route. Second, it is unclear how well the past measurements will accurately predict the future network conditions. Further, how often do the network conditions need to be monitored and the measurements updated? The minimum recovery time from one failed path to a new path is the same as the probing frequency, which is often over 5 minutes and unacceptable for real-time traffic.
The present invention relates to improvements in the prior art that help enterprises deal with the failures, losses, and delays that occur in SP networks. In particular, the preferred embodiment of the present invention incorporates a form of “service-aware routing” that duplicates certain packets (e.g., VoIP) for simultaneous transmission to multiple WAN links, e.g. multiple service providers. After traversing the service provider networks, only the first-to-arrive packets are kept and the later-arriving copies are discarded. Consequently, the present invention helps reduce the impact of WAN or SP failures, losses, and delays on real-time applications such as VoIP. The present invention works also on multiple LAN links.